1. Field of the Invention
The present invention pertains to an antistatic viewfinder, and more particularly, to a viewfinder used in such things as a camera using silver halide film, an electronic image recording device or binoculars.
2. Description of the Prior Art
Conventionally, either glass or resin has been used in optical systems, but the use of resin has increased in recent years due to its superior malleability and lower cost. Normally, resin easily attracts static atmospheric charge, allowing dust and dirt particles to easily adhere to the surface of the resin via adsorption. Consequently, if for example optical members of a viewfinder equipped with an eyepiece are constructed of resin, the problem arises that the dust and dirt particles that have become adhered to area around the image plane of the object image become enlarged and easily visible.
In response to this problem, one countermeasure is to clean the surfaces of the optical members prior to their incorporation into the optical systems and make the viewfinder airtight, thereby preventing dust and dirt particles from adhering to the optical members. Another countermeasure is to lower the surface resistance of the optical member by either applying an antistatic coating or mixing an antistatic agent into the resin, thereby making It more difficult for the surfaces to become charged and for dust and dirt particles to adsorb to them.
However, because adsorption Is operating on the dust and dirt particles adhering to the surfaces of the optical member due to electrostatic charging of the optical member, it is very difficult to eliminate them completely even if the surfaces of the optical members are cleaned. Moreover, the application of an antistatic coating does not affect the dust and dirt particles that are already adhering to the surfaces of the optical member, and increases the cost of manufacture as well. In addition, with the method involving the mixture of an antistatic agent Into the resin, while the antistatic agent continues to seep out toward the optical member surfaces in small amounts and an antistatic property, i.e., an anti-charging property, is maintained, this continues for only about a year. Further, there is another problem that the dust and dirt particles that have adhered to members other than the optical members In the viewfinder block, such as holders or the field mask, move to the surfaces of the optical members.